Fluorinated Reduced Graphene Oxide-Encapsulated ZnO Hollow Sphere Composite as an Efficient Photocatalyst with Increased Charge-Carrier Mobility.

Zinc oxide (ZnO) hollow spheres were prepared by the hydrothermal method and encapsulated with fluorinated reduced graphene oxide (FRGO) using a tetra- n-butylammonium bromide (TBAB) linker to give an FRGO/ZnO composite. X-ray diffraction and microscopic studies revealed their hexagonal-wurtzite structure, spherical morphology, and size of the crystallite to be 26.7 nm. Diffuse reflectance UV-visible spectroscopy showed an optical band gap and semiconductive nature of the composite. Atomic force microscopy images show the surface topography of FRGO-encapsulated ZnO hollow spheres. The photoluminescence spectra depicted the electron-hole pair recombination order to be ZnO > RGO/ZnO > FRGO/ZnO. The electrochemical impedance spectroscopy (EIS) demonstrates the increased charge-carrier mobility of the FRGO/ZnO composite; the Rct values of ZnO, RGO/ZnO, and FRGO/ZnO were found to be 6.18 × 103, 4.07 × 103, and 3.45 × 103 Ω, respectively. All the three materials were employed as photocatalysts in the degradation of methylene blue under UV-365 nm radiation and the results exposed the higher photocatalytic activity of reduced fluorinated graphene oxide/ZnO than RGO/ZnO and bare ZnO hollow spheres. The increased photocatalytic activity of the composite is due to the enhanced vectorial transport of charge carriers at the interface of the FRGO/ZnO composite and suppression of charge-carrier recombination. The presence of fluorine in the RGO sheet introduces additional defects and leverages heterogeneous electron transport. In turn, mobility of light-generated charge carriers is increased and results in suppression of their recombination, which facilitates the photocatalytic process.

Insights into protein-ionic liquid interaction: A comprehensive overview on theoretical and experimental approaches.

Owing to highly tunable nature, ionic liquids are nesting stance in the scientific community for a wide variety of applications ranging from electrochemistry to product purification, from chemical and biomedical applications to biotechnological interventions and proteomics. Proteins are unstable in its native form and several attempts have been made to stabilize them by addition of various additives. This review focusses on the studies conducted to improve protein stability with ionic liquids along with an emphasis on the mechanism of interaction. This review also specifies and discusses about the brief introduction to ionic liquids, evolution of first-, second-, and third generation of liquids over the years and their selection criterion and applications. Though, there are several elegant reviews available on proteins-ionic liquids interaction, this review systematically highlights the effect of ionic liquids viz., imidazolium, ammonium, phosphonium and choline-based ionic liquids (amino acid-based anions & classical anions) on fibrous proteins viz., collagen and keratin and globular proteins viz., bovine serum albumin and cytochrome c. Thus, this review elaborates the thorough investigations conducted to explore the stabilizing properties of ionic liquids over fibrous and globular proteins.

Molecular dynamics investigations on the effect of D amino acid substitution in a triple-helix structure and the stability of collagen.

Studies on the structure and stability of peptides and proteins during l-->d configurational change are certainly important for the designing of peptides with new biological activity and protein engineering. The l-->d amino acid (d AA) changes have been observed in aged proteins such as collagen. Hence, in this study, an attempt has been made to explore the effect of the replacement of l amino acid (l AA) in the model collagen-like peptides with d AA and the origin of structural stability (destability) has been traced using the molecular dynamics (MD) method employing the AMBER force field. Our results reveal that the substitution of d AA produces a large local disruption to the triple-helical structure. Formation of a kink (bulge) at the site of substitution is observed from the detailed analysis of MD trajectory. However, this local perturbation of kinked helix changes the direction of the helices and affects the relative orientation of the respective AA residues for helix-helix interaction, enough to affect the overall stability of the model collagen-like peptide. The destabilization energy per d Ala substitution is 7.87 kcal/mol, which is similar to the value for the Gly-->Ala mutation in collagen. Since the Gly-->Ala mutation is involved in genetic disorders such as osteogenesis imperfecta (OI), the l-->d configurational change may produce a similar effect on collagen.

Probing visible light induced photochemical stabilization of collagen in green solvent medium.

Crosslinking of proteins such as collagen for enhanced stability and mechanical properties is an intriguing area in the context of both biomedical and industrial applications. Herein, we have shown the crosslinking of collagen fibers using visible light in a green solvent, ethanol, in the presence of photosensitizers such as methylene blue (Mb) and erythrosine B (Eb). The visible light induced crosslinking increases the shrinkage temperature of collagen fibers from 67 to 100 °C in a concentration dependent manner (1.0 mM Mb/Eb) as revealed by differential scanning calorimetry. Such manifestation was possible only in the presence of ammonium persulphate, a photo-initiator, which has been corroborated through enzymatic degradation, fluorescence and Raman spectroscopic studies. We have also demonstrated that the photoexcited tyrosine moiety of collagen fibers form di-tyrosine during the crosslinking between the peptide chains through steady-state and time-resolved fluorescence measurements. The results suggest a new and efficient photocrosslinking technique to stabilize proteins for diverse applications.

A potential new commercial method for processing leather to reduce environmental impact.

INTRODUCTION: Current leather processing method involves dehairing and fibre opening employing lime and sulphide, which results in higher negative impact on the environment due to its uncleanness. This method of dehairing and fibre-opening process accounts for nearly 70-80% biochemical oxygen demand and chemical oxygen demand (COD) in tannery wastewater and also the generation of H(2)S gas. MATERIALS AND METHODS: Hence, an attempt has been made to reduce the environmental impact of the leather processing through a biochemical approach, employing proteolytic enzyme and sodium metasilicate for performing the above process more cleanly. RESULTS AND DISCUSSION: The developed process exhibits significant reduction in environmental parametres such as COD and total solid loads by 55% and 25%, respectively. This method completely avoids the formation of lime sludge. CONCLUSION: The functional properties of the leathers are also on par with conventionally processed leathers. Further, the process seems to be commercially viable.

Choline-Based Amino Acid ILs-Collagen Interaction: Enunciating Its Role in Stabilization/Destabilization Phenomena.

Given the potential of productive interaction between choline-based amino acid ionic liquids (CAAILs) and collagen, we investigated the role of four CAAILs, viz., choline serinate, threoninate, lysinate, and phenylalaninate, and the changes mediated by them in the structure of collagen at different hierarchical orderings, that is, at molecular and fibrillar levels. The rheological, dielectric behavior and the secondary structural changes signify the alteration in the triple helical structure of collagen at higher concentrations of CAAILs. A marginal swelling and slight decrease in the thermal stability of rat tail tendon collagen fibers were observed for choline serinate and threoninate, albeit distortions in banding patterns were noticed for choline lysinate and phenylalaninate, suggesting chaotropicity of the ions at the fibrillar level. This signifies the changes in the hydrogen-bonding environment of collagen with increasing concentrations of CAAILs, which could be due to competitive hydrogen bonding between the carbonyl group of amino acid ionic liquids and the hydroxyl groups of collagen.

Role of green tea polyphenols in the inhibition of collagenolytic activity by collagenase.

Inhibitory effect of green tea polyphenols viz., catechin and epigallocatechin gallate (EGCG) on the action of collagenase against collagen has been probed in this study. Catechin and EGCG treated collagen exhibited 56 and 95% resistance, respectively, against collagenolytic hydrolysis by collagenase. Whereas direct interaction of catechin and EGCG with collagenase exhibited 70 and 88% inhibition, respectively, to collagenolytic activity of collagenase against collagen and the inhibition was found to be concentration dependent. The kinetics of inhibition of collagenase by catechin and EGCG has been deduced from the extent of hydrolysis of (2-furanacryloyl-L-leucyl-glycyl-L-prolyl-L-alanine), FALGPA. Both catechin and EGCG exhibited competitive mode of inhibition against collagenase. The change in the secondary structure of collagenase on treatment with catechin and EGCG has been monitored using circular dichroism spectropolarimeter. CD spectral studies showed significant changes in the secondary structure of collagenase on treatment with higher concentration of catechin and EGCG. Higher inhibition of EGCG compared to catechin has been attributed to the ability of EGCG to exhibit better hydrogen bonding and hydrophobic interaction with collagenase.

Factors influencing activity of enzymes and their kinetics: bioprocessing of skin.

The conventional chemically based method of dehairing and fiber-opening discharges an enormous amount of pollutants in the processing of skins. Hence, bioprocessing of skin through a two-step process, dehairing using protease and fiber opening using alpha-amylase, has been developed. However, because this process involves two steps, we characterized commercial protease and alpha-amylase for their optimum activity and determine the influence of one enzyme on the activity of the other, in order to develop an integrated enzymatic dehairing and fiber-opening process. The influence of various factors, substrate concentration, time, pH, and temperature, on the activity of both protease and alpha-amylase was determined. Furthermore, the activity of protease on mixing with alpha-amylase and vice versa was investigated. It was found that there was no significant change in the activity of one enzyme in the presence of the other. Lineweaver-Burk plots showed K(m) and V(max) values of 31.6 mg/mL and 0.0106 mg/(mL@min) for protease and 8.79 mg/mL and 0.0912 mg/(mL@min) for alpha-amylase. This study provides substantial evidence for integrating the enzyme-based dehairing and fiber-opening processes using both the selected protease and alpha-amylase in one step.

Biodegradability of leathers through anaerobic pathway.

Leather processing generates huge amounts of both solid and liquid wastes. The management of solid wastes, especially tanned leather waste, is a challenging problem faced by tanners. Hence, studies on biodegradability of leather become imperative. In this present work, biodegradability of untanned, chrome tanned and vegetable tanned leather under anaerobic conditions has been addressed. Two different sources of anaerobes have been used for this purpose. The effect of detanning as a pretreatment method before subjecting the leather to biodegradation has also been studied. It has been found that vegetable tanned leather leads to more gas production than chrome tanned leather. Mixed anaerobic isolates when employed as an inoculum are able to degrade the soluble organics of vegetable tanned material and thus exhibit an increased level of gas production during the initial days, compared to the results of the treatments that received the anaerobic sludge. With chrome tanned materials, there was not much change in the volume of the gas produced from the two different sources. It has been found that detanning tends to improve the biodegradability of both types of leathers.

Stabilization of collagen using plant polyphenol: role of catechin.

Collagen, a unique connective tissue protein finds extensive application as biocompatible biomaterial in wound healing, as drug carriers, cosmetics, etc. A work has been undertaken to study the stabilization of type I collagen using the plant polyphenol catechin. Catechin treated collagen fibres showed a shrinkage temperature around 70 degrees C implying that catechin is able to impart thermal stability to collagen. Catechin treated collagen fibres has been found to be stable even after treatment with high concentration of the secondary structural destabilizer, urea. Circular dichroism studies revealed that there is no major alteration in the structure of collagen on treatment with catechin. The study has demonstrated the involvement of hydrogen bonding and hydrophobic interactions as the major forces involved in the stabilization of collagen by the plant polyphenol, catechin.

Electrostatic Forces Mediated by Choline Dihydrogen Phosphate Stabilize Collagen.

Cross-linkers aid in improving biostability of collagen via different mechanisms. Choline dihydrogen phosphate (cDHP), a biocompatible ionic liquid, has been reported as a potential cross-linker for collagen. However, its mechanism is yet unclear. This study explores the effect of cDHP on the physicochemical stability of collagen and nature of its interaction. Dielectric behavior of collagen-cDHP composites signifies that cDHP enhances intermolecular forces. This was demonstrated by an increase in cross-linked groups and high denaturation temperature of collagen-cDHP composites. XRD measurements reveal minor conformational change in helices. Molecular modeling studies illustrate that the force existing between collagen and cDHP is electrostatic in nature. Herein, it is postulated that dihydrogen phosphate anion attaches to cationic functional groups of collagen, resulting in closer vicinity of various side chains of collagen, forming physical and chemical cross-links within collagen, contributing to its structural stability. Our study suggests that dihydrogen phosphate anions can be employed for developing a new class of biocompatible cross-linkers.

Effect of ionic liquids on the different hierarchical order of type I collagen.

The effect of ionic liquids (ILs) on proteins has been gaining huge interest due to easy tunability of cation and anion for generating the desired effect. This study explores the effect of alkyl imidazolium chloride ILs on collagen at molecular, inter-fibrillar and skin matrix level. Circular dichroic studies reveal that at the molecular level, the secondary structure of collagen was not affected by imidazolium ILs and there was no change in thermal stability as well. However, collagen at the inter-fibrillar level behaved differently. With increase in concentration of ILs, remarkable decrease in thermal stability of rat tail tendon (RTT) collagen fibers with marginal swelling effect was seen. SEM micrographs of skin matrix treated with IL show opening up of pores. This kind of exquisite behavior of ILs at different hierarchal order of collagen indicates that ILs are endowed with potential lyotropic action, which can be judiciously employed for biomedical applications.

Can green solvents be alternatives for thermal stabilization of collagen?

"Go Green" campaign is gaining light for various industrial applications where water consumption needs to be reduced. To resolve this, industries have adopted usage of green, organic solvents, as an alternative to water. For leather making, tanning industry consumes gallons of water. Therefore, for adopting green solvents in leather making, it is necessary to evaluate its influence on type I collagen, the major protein present in the skin matrix. The thermal stability of collagen from rat tail tendon fiber (RTT) treated with seven green solvents namely, ethanol, ethyl lactate, ethyl acetate, propylene carbonate, propylene glycol, polyethylene glycol-200 and heptane was determined using differential scanning calorimetry (DSC). Crosslinking efficiency of basic chromium sulfate and wattle on RTT in green solvents was determined. DSC thermograms show increase in thermal stability of RTT collagen against heat with green solvents (>78°C) compared to water (63°C). In the presence of crosslinkers, RTT demonstrated thermal stability >100°C in some green solvents, resulting in increased intermolecular forces between collagen, solvent and crosslinkers. The significant improvement in thermal stability of collagen potentiates the capability of green solvents as an alternative for water.

Calorimetric analysis of gelatine-glycosaminoglycans blend system.

Gelatine is one of the most valuable natural polymers used for drug delivery applications. Gelatine-GAGs based composite system has been shown to act as good scaffolds for tissue engineering. The objective of the present study is to investigate the calorimetric properties of microporous gelatine-GAGs based blend, which were modified by co-crosslinking with a naturally occurring crosslinking agent genipin. The melting temperature (T(m)), enthalpy change (ΔH(m)) and heat capacity change (ΔC(p)) were systematically calculated over the experimentally observed systems using differential scanning calorimeter (DSC). The thermoporometry results suggest that the concentration of the glycosaminoglycans plays an important role in the pore size distribution of the blend matrices. The circular dichroism (CD) spectroscopy study, scanning electron microscopy (SEM) studies provide the valuable information about the structural features of the biodegradable blend that can be utilized for various biomedical applications. The results provide new insights into the thermal stability of blend and suggest potential strategies for its manipulation.